38 UNIVERSITY OF MISSOURI STUDIES [180 



trees allows a weedy light-loving herbage to come in, which is 

 more or less mingled with Poa pratensis. The forest thence 

 becomes a permanent pasture. 



The mesophytic sylvan flora consists of a mixture of ar- 

 boreal, fruticose, and herbaceous elements. These are not uni- 

 form in their distribution or in their composition, though in 

 general the same species are found in the various situations, but 

 in such diverse proportions that the aspect often is quite dif- 

 ferent. The mesophytic forest has a wide range of physio- 

 graphic conditions, of soils, of density and of openness. The 

 character of the forest floor differs also according to the season, 

 the vernal flora being mainly of northern origin and of strictly 

 sylvan species, the autumnal consisting largely of Compositae 

 of southwestern origin and of prairie species. It must be borne 

 in mind, however, that there are certain herbs, notably the 

 grasses, sedges and ferns, that remain as dominant factors 

 throughout the year. These give unity to the herbaceous flora 

 and together with the trees and shrubs form the permanent char- 

 acteristics of the sylva. 



Before entering into detailed descriptions of minor plant 

 groupings, it is well to consider the sylva as a whole. Only one 

 plant society is present, though there are a number of subasso- 

 ciations. 



a. Sylvales quercoides. The oak society of the sylva 

 consists of the various species of oak {Quercus) as primary, the 

 various hickories {Carya) and the walnut (Juglans nigra) be- 

 ing next in importance. Other trees occurring in more or less 

 abundance are species of Fraxinus, Acer, Ulmus, Celtis, Gyni- 

 nodadiis, Gleditschia, Aesculns, and Diospyros. Of small trees, 

 or arborescent plants, Ostrya, Carpinus, Cornus, Cercis, Vibur- 

 num, Sassafras, and Mespilus are common, some in one portion 



